Here it is:
Find x and y.
I've tried this for ages but the answers are and
That's a solution for both equations.....but x<>c and y<>-a
There are many other similar cases.
Did I miss something?
Also, equations can be re-arranged this way:
ax + bx + cy = bc 
-ax - by - cy = ab 
bx - by = ab + bc
x - y = a + c